The ability of the tooth to resist catastrophic fracture throughout its functional life within the oral cavity is not well understood. When a dental fracture occurs and is usually diagnosed as "cracked-tooth-syndrome", it may become intensely painful to a patient, depending on the type and extent of the lesion. The purpose of this research is to attempt to determine the morphological and physiological explanation of the "cracked-tooth-syndrome". Current research has shown that the dentin-enamel junction (DEJ) is a unique zone between two highly dissimilar hard tissues capable of arresting the propagation of enamel cracks into dentin and thus toughening the crown of the tooth as a whole. Important hypotheses to be tested therefore would attempt to explain how the DEJ act globally throughout the tooth to resist catastrophic fracture, along with determining the conditions required for failure of the DEJ to occur. Thus, the first phase of research would involve a series of analyses designed to test the strength of the DEJ and map the morphology of the DEJ. Once the anatomical basis has been established, a second phase of experiments should be carried out to test the relationship between the anatomy and its mechanical role. Such experiments would involve fracture toughness evaluation using both monolithic and interfacial techniques, digital image analysis, scanning electron microscopy, and computer simulations (i.e. finite element method). The final phase could consist of the testing of hypotheses by means of numerical models which are otherwise difficult to assess technically. These models would be created through state-of-the-art three-dimensional digitizers and would be validated prior to their interrogation.